The present invention relates to a running energy recovery system for use on a motor vehicle which is powered by a gasoline engine.
Various proposals have been made to recover the energy of exhaust gases emitted from engines on motor vehicles.
For example, Japanese Laid-Open Patent Publication No. 60(1985)-195329 discloses an exhaust energy recovery system wherein a rotary electric machine which can selectively operate as a motor or a generator is mounted on the rotatable shaft of a turbocharger that is driven by the energy of exhaust gases emitted from an engine. In a low-speed, high-load operating range of the engine, the rotary electric machine operates as a motor which increases the rotational speed of the turbocharger for increasing the boost pressure. In a high-speed or low-load operating range of the engine, the rotary electric machine operates as a generator which generates electric energy that will be recovered.
Japanese Laid-Open Patent Publication No. 59(1984)141714 also discloses an energy recovery system which comprises a first rotary electric machine selectively operable as a motor or a generator and mounted on the rotatable shaft of a turbocharger, and a second rotary electric machine selectively operable as a motor or a generator and coupled to the rotatable shaft of the engine on a motor vehicle. When the first rotary electric machine operates as a generator, electric power generated thereby is supplied to the second rotary electric machine to operate it as a motor, so that the energy of exhaust gases emitted from the engine can be returned to the engine. When the motor vehicle is braked, the second rotary electric machine operates as a generator which converts the braking energy into electric energy to be recovered.
Gasoline engines are controlled such that the ratio of intake air to fuel (A/F ratio) will be a stoichiometric A/F ratio. When the gasoline engine operates under a low load, the opening of the throttle valve is restricted to reduce the rate of intake air, and hence the rate of exhaust gases is also small. Therefore, the rotary electric machine of the energy recovery system disclosed in the former publication has a little chance to generate electric power in a low-load operating range of the engine. Particularly when the accelerator pedal is released or is no longer depressed at the time the motor vehicle is decelerated or running downhill, the opening of the throttle valve is minimized to reduce the rate of intake air, and hence the rate of exhaust gases led to the turbocharger is greatly reduced. Consequently, any work done by the turbocharger becomes almost zero, and it becomes impossible to recover the energy in the form of generated electric power.
According to the energy recovery system disclosed in the latter publication, when the motor vehicle is braked, the rotary electric machine coupled to the rotatable shaft of the engine operates as a generator which recovers electric energy from the braking energy. This energy recovery system is however complex and highly costly since the second rotary electric machine has to be coupled to the rotatable shaft of the engine.